212 
light reflected from the film is passed through a lens, and an 
image formed upon a screen. When the bands of colour are 
seen descending from the upper part of the film, a current from 
fifty Grove’s cells is passed through it. If the current flows 
downwards the bands of colour move more quickly than before ; 
if it flows upwards their motion is checked and they begin to 
ascend. The cause of this curious fact is still unknown. It 
may either be analogous to the phenomenon known as the 
““migration of the ions,” or it may be a secondary effect due to 
a change in the surface tension. 
The general relation of the results attained by these investiga- 
tions as to the question of the size of molecules is interesting. 
Sir William Thomson has expressed the opinion that 2x 10° § 
mm. and o’or x 107® mm. are superior and inferior limits respec- 
tively to the diameter of a molecule. Van der Waals has been 
led, from considerations founded on the theory of gases, to give 
0°28 x 10-® mm. as an approximate value of the diameters of the 
molecules of the gases of which the atmosphere is composed. 
The number of molecules which could be placed side by side 
within the thickness of the thinnest soap film would, according 
to these various estimates, be 4, 26, and 720 respectively. The 
smallness of the first of these numbers, especially when it is 
remembered that the liquid used on some occasions was of a 
highly complex character, containing water, glycerine, and soap, 
points to the conclusion that the diameter of a molecule is 
considerably less than 2 x 1076 mm. 
THE FAUNA OF THE SEASHORE? 
‘THE marine fauna of the globe may be divided into the 
littoral, the deep-sea, and the pelagic faunas. Of the three 
regions inhabited by these faunas, the littoral is the one in 
which the conditions are most favourable for the development of 
new forms through the working of the principle of natural 
selection. As Prof. Lovén writes, ‘“‘ The littoral region com- 
prises the favoured zones of the sea where light and shade, a 
genial temperature, currents changeable in power and direction, 
a rich vegetation spread over extensive areas, abundance of food, 
of prey to allure, of enemies to withstand or evade, represent 
an infinitude of agents competent to call into play the tendencies 
to vary which are embodied in each species, and always ready 
by modifying its parts to respond to the influences of external 
conditions.” It is consequently in this littoral zone where the 
water is more than elsewhere favourable for respiration, and 
where constant variation of conditions is produced by the tides, 
that all the main groups of the animal kingdom first came into 
existence ; and here also, probably, where the first attached 
and branching plants were developed, thus establishing a 
supply of food for the colonisation of the region by animals. 
The animals inhabiting the littoral zone are most variously 
modified, to enable them to withstand the peculiar physical 
conditions which they encounter there. Hence the origin of all 
hard shells and skeletons of marine invertebrata, various adapta- 
tions for boring in sand, the adoption of the stationary fixed con- 
dition, and similar arrangements. Almost all the shore forms of 
animals, however inert in the adult condition, pass through in 
embryological development free-swimming larval stages which 
are closely alike in form for very widely different groups of 
animals. Thus the oyster and most other mollusca of all 
varieties’ and shapes when adult develop from a free-swimming 
pelagic trochosphere larya, and so do many annelids. Such 
larvee cannot be of subsequent origin to the adults of which they 
are phases. If such were the case, they would not have become 
so closely alike in structure. In reality they represent the 
common ancestors from which all the forms in which they occur 
were derived, and as all these larve are pelagic in habits and 
structure, it follows that the inhabitants of the shores were 
derived from pelagic ancestors. The earliest plants were also 
probably free-swimming. 
In the case of the cirripedia there can be no doubt, from the 
history of their development, that they were originally pelagic, 
and have become specially modified for coast life ; and in the 
case of the echinoderms the only possible explanation of the 
remarkable similarity of the larval forms of the various groups of 
widely differing adults is that these pelagic larvae represent a 
common ancestor of the group. The madreporarian corals all 
spring from a pelagic larva. The colonial forms probably owe 
their origin and that of their skeletons to the advantage gained 
1 Abstract of lecture at the Royal Institution by Prof. H. N. Moseley, 
M.A., F.R.S. 
NATURE 
[Fuly 2, 1885 
by them in the formation of reefs, and the increase in facilities 
of respiration consequent on the production of surf. In the deep 
sea they are very scarce. 
The vertebrata are sprung from a very simple free-swimming 
ancestor, as shown by the ciliated gastrula stage of Amphioxus. 
The ascidians afford another evident instance of the extreme 
modification of pelagic forms for littoral existence. 
The peculiar mode of respiration of vertebrata by means of 
gill-slits occurs in no other animal group except in Balanoglossus, 
which will probably shortly be included amongst vertebrata. 
Possibly gill-slits as a respiratory apparatus first arose in a 
littoral form, such as Balanoglossus, and hence their presence at 
the anterior end of the body, that nearest to the surface in an 
animal buried in sand. The connection of Balanoglossus with 
the echinoderms through Tornaria is very remarkable. Possibly 
Amphioxus once had a Tornaria stage, and has lost it just as 
one species of Balanoglossus has lost it, as Mr. Bateson has 
lately discovered. 
The littoral zone has given off colonists to the other three 
faunal regions, The entire terrestrial fauna has sprung from 
colonists contributed by the littoral zone. Every terrestrial 
vertebrate bears in its early stages the gill-slits of its aquatic 
ancestor. All organs of aérial respiration are mere modifications 
of apparatus previously connected with aquatic respiration, ex- 
cepting, perhaps, in the case of Tracheata, tracheze being most 
likely modifications of skin-glands, as appears probable from 
their condition in Peripatus. The oldest known air-breathing 
animals are insects and scorpions, which have lately been found 
in Silurian strata. Prof. Ray Lankester believes the Jungs of 
scorpions to be homogeneous with the gill-plates of Limulus. 
Birds were possibly originally developed in connection with 
the seashore, and were fish-eaters like the tooth-bearing Hes- 
perornis. 
The fauna of the coast has not only given rise to the terrestrial 
and fresh-water fauna; it has from time to time given additions 
to the pelagic fauna in return for having thence derived its own 
starting-points. It has also received some of these pelagic forms 
back again, to assume a fresh littoral existence. 
The deep-sea fauna has probably been formed almost entirely 
from the littoral, not in the remotest antiquity, but only after 
food derived from the drs of the littoral and terrestrial faunas 
and floras became abundant. 
It is because all terrestrial and deep-sea animal forms have 
passed through a littoral phase of existence, and that the littoral 
animals retain far better than those of any other faunal region 
the recapitulative larval phases by means of which alone the true 
histories of their origins can be recovered, that marine zoolog*cal 
laboratories on the coast have made so many brilliant discoveries 
in zoology during late years. 
The lecturer concluded by appealing for as istance, in the way 
of subscriptions, to the funds of the Marine Biological Associa- 
tion of Great Britain, the object of which is to construct a marine 
laboratory on the English coast for the purpose of researches 
such as those referred to. England is at present without any 
such laboratory, although nearly all Continental countries possess 
them. 
THE PHILOSOPHICAL SOCIETY OF 
GLASGOW 
THE Proceedings of this Society for 1884-85 have just been 
issued in a volume of 408 pages, with six plates and two 
maps. The followin® are the principal contributions :—On 
feeling and perception of relation, by Dr. H. Muirhead, 
President ; on the proper motions of the stars, by Prof. Grant ; 
on the first editions of the chemical writings of Democritus and 
Synesius, by Prof. Ferguson; on the composition of ocean 
water, by Prof. Dittmar; on the regulation of the supply of 
water to cities and towns, by Mr. W. Key; on a shadowless 
gas ventilator, by Mr. George A. Buchanan ; on African colonies 
and colonisation, by J. E. Carlyle ; a memoir of the late Mr. 
James Napier ; on a new musical instrument, by Mr. Thomas 
Machell ; ona:description of a new Rotiferon, by Mr. W. Milne ; 
on a theory of storm-trayel, by Mr. P. Alexander; on national 
and local precautions against cholera, by Dr. James Christie ; 
on an air or gas thermometer, by Mr. J. J. Coleman ; on some 
experiments on the influence of cold on the putrefactive process, 
by Mr. J. J. Coleman and Prof. McKendrick ; on the liquefac- 
tion of air and other effects of extreme cold, and on artificial 
light and other phenomena of high temperature, by Mr. J. J. 
